configuration is similar to the PPPoE
configuration. The difference between the two configurations is
shown in the configuration outputs illustrated in the Figure :
- VPDN group is enabled for PPPoE (Prior to Cisco IOS
software Release 12.2(13)T), and the ATM PVC is configured for
PPPoE client encapsulation. In the PPPoA configuration, you
must configure proper ATM adaptation Layer 5 (AAL5)
encapsulation on the ATM PVC.
- In the PPPoE client
configuration, you also have to reduce the dialer interface MTU
size from 1500 to 1492.
Content 2.6
Configuring the CPE as the PPPoE or PPPoA Client
2.6.11 Configuring a DSL ATM Interface Figures and
show the steps you use to configure a DSL ATM interface. Use
the dsl operating-mode auto interface configuration
command to specify that the router automatically detects the
DSL modulation that the service provider is using and sets the
DSL modulation to match. An incompatible DSL modulation
configuration can result in failure to establish a DSL
connection to the DSLAM of the service provider. Use the
pvc interface configuration command to set the virtual
path identifier/virtual channel identifier (VPI/VCI) that is
used by the DSL service provider, as shown in the pvc
Parameters table. Settings for the VPI/VCI value on the Cisco
router must match the configuration on the DSLAM of the service
provider switch configuration. ATM uses the VPI/VCI to identify
an ATM VC. pvc Parameters
Parameter
Description Vpi VPI from the service provider
Vci VCI from the service provider The encapsulation
method must correspond with the method configured on the
aggregation router. The Encapsulation Commands table shows the
available commands.
Encapsulation Commands
Command Description encapsulation aal5mux ppp
dialer Sets the encapsulation for PPPoA, which uses AAL5 in
the MUX mode dialer pool-member number Links
the ATM interface to a dialer interface Use the dialer
pool-member command to specify which dialer interfaces can
use the ATM physical interface on the Cisco router. Figure
shows an example of a complete PPPoA configuration. The example
presents the complete PPPoA configuration with PAT, DHCP
services, MTU adjustments, and static default routing.
Content 2.7 Troubleshooting Broadband ADSL
Configurations 2.7.1 Troubleshooting Layers 1,
2, and 3 ADSL service problems can reside at Layer 1, Layer
2, or Layer 3. Troubleshooting should start by determining
which ADSL service layer is failing. To determine which layer
has a problem, use a bottom-up approach; that is, start
troubleshooting at Layer 1 and move to subsequent layers as
required. Figure illustrates this approach.
Content
2.7 Troubleshooting Broadband ADSL
Configurations 2.7.2 Determine Whether the
Router Is Properly Trained to the DSLAM Start
troubleshooting Layer 1 by verifying whether a Cisco Systems
CPE router is trained to the DSLAM in the CO by using the
show dsl interface atm command. When a router is
successfully trained to the DSLAM, the modem status field has
the value Showtime. Along with that value, the command
also displays the upstream and downstream speed in kbps (in the
row Speed, the Interleave or Fast columns will have a nonzero
value). Figure is an example of the output from a properly
trained modem. If the modem and router are properly trained,
move troubleshooting efforts to Layer 2. When the router is not
properly trained, as shown in the following output, the problem
is at Layer 1, and a solution needs to be found at this layer.
Router#show dsl interface atm 0
Line not activated:
displaying cached data from last activation
Log file of
training sequence:
<...rest of the output
omitted...>
Content 2.7 Troubleshooting
Broadband ADSL Configurations 2.7.3
Troubleshooting Layer 1 Issues You can monitor the status
of the ATM interface on the router by checking the status of
the Carrier Detect (CD) light on the router’s interface panel:
- If the CD light is on, proceed to Layer 2
troubleshooting.
- If the CD light is off,
continue with Layer 1 troubleshooting.
Next, use the
show interface atm privilege level command from the
enable mode of the router to check the status of the ATM
interface on the router. This command appears in Figure . If
the ATM interface status is down and the line protocol is down,
the router is not seeing a carrier on the ADSL line. Such a
status usually indicates two possible issues: - The
active pins on the DSL wall jack may be incorrect. For example,
the registered jack-11 (RJ-11) connector provides an xDSL
connection to an external media via a standard RJ-11 6-pin
modular jack.
- The service provider may not be
providing DSL service on this wall jack.
The Cisco
router uses a standard RJ-11 cable to provide the ADSL
connection to the wall jack. The center pair of pins on the
RJ-11 cable carries the ADSL signal (pins 3 and 4 on a 6-pin
cable, or pins 2 and 3 on a 4-pin cable). If the wall jack is
using the correct pins, and the ATM interface is still down and
the line protocol is down, replace the RJ-11 cable between the
DSL port and the wall jack. If the interface is still down and
the line protocol is down after you have replaced the RJ-11
cable, contact the service provider to verify that ADSL service
has been enabled on the wall jack you are using. The show
interface atm command also shows whether the interface is
administratively disabled. If such a case exists, enable the
interface by using the no shutdown command under the
interface configuration mode.
Content 2.7
Troubleshooting Broadband ADSL Configurations
2.7.4 Determining the Correct DSL Operating Mode If
everything that you have checked up to now in the Layer 1
troubleshooting procedure is verified and is operating
properly, the next step is to ensure that the correct DSL
operating mode is being used. Check with the service provider
whether the DSLAM supports the particular DSL chipset (for
example, Alcatel) and the configured modulation method of the
deployed Cisco CPE DSL router. If the DSL modulation being used
by the service provider is unknown, Cisco recommends using the
default auto operating mode to autodetect the modulation type.
Run the auto operating mode using this command (see the dsl
operating-mode Parameters table for details): dsl
operating-mode {auto | ansi-dmt | itu-dmt | splitterless}
dsl operating-mode Parameters
Parameter Description auto Configures the
ADSL line after auto negotiating with the DSLAM located at the
CO; this is the default operating mode ansi-dmt
Configures the ADSL line to use the ANSI T1.413 Issue 2 mode
itu-dmt Configures the ADSL line to use the G.992.1
mode splitterless Configures the ADSL line to use the
G.992.2 (G.lite) mode If problems persist and the router has
been properly configured, proceed to Layer 2 examination and
troubleshooting.
Content 2.7 Troubleshooting
Broadband ADSL Configurations 2.7.5
Troubleshooting Layer 2 Issues After establishing that
Layer 1 is operating correctly, the troubleshooting can
continue at Layer 2. First, check whether a permanent virtual
circuit (PVC) is configured at the DSLAM by using the ping
atm interface atm command. This command sends Operation,
Administration, and Maintenance (OAM) F5 loopback packets to
the DSLAM. A successful ping designates that a PVC is
configured at the DSLAM. Next, check whether the correct
VPI/VCI values are configured on the router, by using the
debug atm events command. The output shows the VPI/VCI
values that the DSLAM expects. During the debug process, use
another working Internet connection and begin to ping the
static IP address assigned by your Internet service provider